Great advances in radiological imaging of spinal tumors have occurred over the past 20 years: imaging is now a crucial component in diagnosis and treatment planning.
A variety of imaging modalities are now widely available; computed tomography (CT) and magnetic resonance (MR) are the most helpful imaging tools for early detection of a spinal tumor. Magnetic resonance is often used as the primary diagnostic imaging tool and is the preoperative study of choice.1
The need for biopsy may be obviated because of increasingly accurate preoperative histological diagnosis by MR. Magnetic resonance imaging (MRI) and histological diagnoses are concordant 70% of time.2
Staging Staging of spinal tumors, such as musculoskeletal lesions, is based on clinical and histology as well as imaging characteristics. Magnetic resonance is crucial in evaluation and diagnosis.3 staging systems adopted by the Musculoskeletal Tumor Society and American Joint Committee for Cancer Staging and End Results Reporting was derived from Enneking et al.4,5 staging system declared that standard treatments (surgical and adjuvant therapies) should be implemented on the basis of risk of local recurrence and metastasis. The Weinstein-Boriani-Biagini system further characterized particular lesions on a number of factors including the radiographic grade, angiogram, and CT scan.6 staging system.7 8
Spinal tumors may conveniently be grouped into categories as determined by the neoplasm's location and histology. A variety of "pseudotumors" or benign conditions exist that mimic tumors of the spinal axis; awareness and knowledge of these tumors is important to avoid unnecessary biopsy. A full discussion on "pseudotumors" of the spine is outside the scope of this paper. Intramedullary, intradural extramedullary, and extradural tumors demand tailored treatment which may vary dependent on age, patient's desires and institution.
MATERIALS AND METHODS
Imaging Techniques
Plain Film Radiography
Plain film radiographs are usually included in the initial evaluation of patients with spinal tumors, providing information about osseous anatomy: alignment, bone matrix, bone destruction, sclerosis, and demineralization. Early lesions may be hard to detect; 30% to 50% of trabecular bone must be lost for a vertebral lesion to be evident on a plain radiograph.9
The benign or malignant nature of the lesion may be inferred from the pattern of bony destruction. Geographic patterns of bone destruction suggest a slowly expanding lesion, typically benign; more rapidly growing tumors produce a moth-eaten appearance; and highly malignant, aggressive lesions produce a permeative pattern of destruction and wide zone of transition.10
Long-standing tumors may demonstrate an enlarged spinal canal with scalloping of the vertebral bodies, pedicle erosion, and thinning of the lamina. For example, scoliosis is common in children with neurofibromatosis type 1 (NF-1) or astrocytomas; the apex of the curvature is frequently to the left rather than the right as is more commonly seen in idiopathic scoliosis.11
Scintigraphy
The most sensitive, albeit nonspecific, test for detecting bone lesions such as primary and metastatic tumors, infections, and fractures is the technetium 99m bone scan. Technetium scans are sensitive to an area of increased osteoid formation and can detect lesions as small as 2 mm, whether in trabecular or cortical bone. These abnormalities must be correlated to more specific imaging modalities. Whole-body scintigraphy is possible for screening and is advantageous over CT or MR. Magnetic resonance is, however, more sensitive than scintigraphy for detecting disease within the vertebral medullary space. F18-fluorodeoxyglucose positron emission tomography can detect, stage malignant lesions and monitor tumor recurrences and may accurately detect metastases more often than conventional bone scintigraphy.
Computed Tomography
Computed tomography is highly sensitive to alterations in bone mineralization and is particularly useful in evaluating cortical bone, for identifying pathological fractures and demonstrating the bony matrix of primary osseous tumors. It is more reliable than plain radiographs in demonstrating bony involvement. The introduction of multidetector CT and high-quality multiplanar reformatting routinely used in spinal imaging has greatly improved diagnostic accuracy. Multidetector computed tomography can detect early trabecular destruction and has been found to be more accurate than MR in the detection of myeloma involvement in the spine.12
Magnetic Resonance Imaging
Magnetic resonance imaging has become the imaging modality of choice for evaluation of tumors of the spine. Superb contrast sensitivity and multiplanar capabilities makes MRI an ideal modality for the evaluation of spinal contents, localizing lesions and greatly assisting in preoperative planning. Contrast-enhanced MR defines the relationship of the tumor to the spinal cord, nerve roots and thecal sac, differentiating tumor from peritumoral edema and cysts, determining tumor extent, and evaluating intrinsic cord signal abnormalities.
For evaluation of the spinal cord, both T1-weighted image (T1WI) and T2-weighted image (T2WI) should be obtained in the axial and sagittal planes. T1-weighted images should be performed precontrast and postcontrast. Coronal imaging is particularly useful in laterally located or multilevel lesions.
Gradient-recalled echo (GRE) sequences are more sensitive in detecting hemorrhage and are especially useful in the setting of trauma. The short-time inversion recovery (STIR) sequence is excellent for evaluating marrow and soft tissue edema, tumor, and intramedullary cord lesions.
Magnetic resonance myelography gives images similar to those obtained by conventional myelography and is a very heavily weighted T2-weighted sequence and produces high signal from cerebrospinal fluid (CSF).
Diffusion-weighted imaging and MR spectroscopy of the spinal cord remain technically difficult. Several limitations include the small size of the cervical cord, susceptibility artifacts, and the need for a large voxel size to obtain sufficient signal. Recently, diffusion weighted imaging has been applied to the spine to distinguish benign from pathological vertebral compression with promising results.13-15
RESULTS
Spinal Tumors can conveniently be grouped into categories as determined by the neoplasm's location as intramedullary, intradural/extramedullary, and extradural (osseous) by location and histology.
Classification
Intramedullary tumors
Ependymoma
Astrocytoma
Ganglioglioma
Hemangioblastoma
Lymphoma
Metastases
Rare tumors-lipoma, glioblastoma multiforme, primitive neuroectodermal tumor (PNET), melanoma, germ cell
Intradural/extramedullary tumors
Nerve sheath tumors
Meningioma
Paragangliomas
Developmental lesions (lipoma and dermoid/epidermoid cysts)
Metastasis
Extradural
Benign
Hemangioma
Osteoid osteoma, osteoblastoma
Aneurysmal bone cysts
Giant cell tumors (GCTs)
Osteochondroma
Malignant
Chordomas
Chondrosarcoma
Osteosarcoma
Ewing Sarcoma/PNET
Metastasis
Intramedullary Tumors
Intramedullary spinal cord tumors account for approximately 25% of spine tumors. Most (90% to 95%) of the intramedullary tumors are malignant and predominantly composed of glial components. Ependymomas are the most common type in adults and astrocytomas in children. Astrocytomas are more frequent in the cervical and the thoracic regions, whereas ependymomas are commonly seen in the region of the conus medullaris, filum terminale, and cauda equina. Symptoms are usually insidious. The neurofibromatosis type 2 (NF-2) patients are at risk for developing intraspinal tumors and may have intramedullary ependymomas in addition to schwannomas and meningiomas. Intramedullary neoplasms are less commonly encountered in NF-1 patients, and they are usually astrocytomas.
Magnetic resonance is the modality of choice in the evaluation of a spinal cord tumor. Spinal cord expansion is the sine qua non of intramedullary tumors. Contrast-enhanced images are important to define the extent of disease and are particularly useful in distinguishing associated "benign" cysts and syrinx from neoplastic involvement. Contrast can help guide biopsy to more active, enhancing parts of the lesion and is essential for postoperative follow-up. Rostral or caudal cysts are commonly associated with intramedullary neoplasms, are considered to be reactive and do not enhance. Intraoperative ultrasound has been used to distinguish solid tumor from these cysts. The reactive cysts are aspirated at the time of resection and commonly resolve after tumor resection. Tumoral cysts, on the other hand, are smaller and irregular with peripheral enhancement and should be excised with the primary tumor.
Tumors associated with a syrinx are usually ependymomas and hemangioblastomas. Altered CSF flow dynamics account for the syrinx. The syrinx is usually at the superior end of the tumor and displaces rather than infiltrates the spinal cord. It resolves spontaneously after surgery.
Ependymomas
Ependymomas represent approximately 60% of all glial-based tumors of the spinal cord and filum terminale. Spinal ependymomas are slow-growing tumors that arise from ependymal cells lining the central canal or from ependymal rests present in the filum terminale or sacral regions. They are usually well circumscribed and do not infiltrate adjacent cord tissue. Cyst formation and hemorrhage is common, especially at the tumor margins. Hemorrhage and calcification are more common than in astrocytomas. The incidence of polar and tumoral cysts is, however, similar to that of other intramedullary tumors and is not a distinguishing feature.
Most of the ependymomas occur in the lumbosacral region but any segment of the spinal cord may be involved. They comprise at least 6 histological subtypes. The most common and classic is the cellular variety, and this is most frequently in the cervical spine. Others include epithelial, tanycytic, myxopapillary, malignant, and melanotic (the least common) types (Fig. 1A-F ). More than 1 histological subtype can exist in the same mass. The myxopapillary subtype tends to occur in the filum terminale as a lesion in the cauda equina, and they have a greater tendency to bleed which may lead to subarachnoid hemorrhage. Subependymomas arise from tanycytes bridging the pial and ependymal layers and are a low-grade, WHO I lesion (Fig. 2A, B ).16,17 18
FIGURE 1: Ependymomas subtypes. A-B, Cellular, the most common subtype. Multiple homogenous and heterogenous intradural enhancing lesions are noted. C-D, Tanycytic variety. Large exophytic mass with proximal reactive cyst. E-F, Myxopapillary subtype. Focal oval-shaped, enhancing mass in the filum terminale.
FIGURE 2: Subependymoma. Unlike ependymomas, they are typically avascular, without cystic change, eccentrically located and demonstrate focal enhancement. A-B, Axial and sagittal fast spin echo. T2WIs show a well-defined mass with an eccentric location as depicted on the axial image. C, Contrast-enhanced sagittal T1WI demonstrates focal nodular enhancement.
Imaging Features
Intramedullary ependymomas tend to be centrally located with sharp margins, unlike astrocytomas which tend to be eccentric and more infiltrative. On T1WIs, ependymomas may be hypointense or isointense to spinal cord and are hyperintense on T2WIs. Myxopapillary ependymomas can be hyperintense on T1 because of mucin content or hemorrhage. Signal heterogeneity may be due to areas of cystic degeneration or hemorrhage. Sometimes, dark caps are seen that are triangular shaped with a hypointense rim on T2WIs at the rostral and caudal tumor margins. The rim represents hemosiderin deposition and has been found to correspond to a pseudocapsule at surgery (Fig. 3A, B ). Contrast is also helpful in visualizing intratumoral cysts because enhancement will be seen around them, unlike around caudal and rostral cysts which do not enhance (Fig. 3C ).
FIGURE 3: Ependymoma. A, Sagittal gradient-recalled echo image showing a heterogenous signal intensity lesion with a fluid-fluid level and focal low signal intensity suggestive of hemosiderin. B, Sagittal fast spin echo T2WI demonstrates the characteristic "cap sign" representing hemosiderin in the pseudocapsule of the large tumoral cyst. Small rostral reactive cyst. C, Postcontrast sagittal T1-weighted MR image demarcates tumor margins. Rim of enhancement is seen around and within the tumoral cyst. Note lack of enhancement around rostral polar cyst.
Homogenous or heterogenous enhancement is noted after contrast enhancement. A cyst with an enhancing nodule may be evident. Lack of enhancement is unusual. Syringohydromyelia may be associated especially with cervical ependymomas.
Treatment
Resection and radiosurgery is indicated.19
Long-term clinical and radiographic follow-up is warranted after surgical resection to exclude tumor recurrence. Recurrence is unusual after complete resection but may occur despite postoperative radiotherapy. Late recurrences can occur even up to 12 years after surgery.
Astrocytomas
Astrocytomas account for approximately 30% of intramedullary tumors. More than half of all astrocytomas are seen in the thoracic region, usually in the upper thoracic cord. They usually involve multiple segments. Holocord involvement is more common in children.
Like their supratentorial counterparts, spinal astrocytomas are graded according the WHO. Unlike supratentorial astrocytomas, tumors arising in the spinal cord are low grade, up to 90% are grade I (pilocytic) or II (low grade of fibrillary).20
Astrocytomas are typically eccentric within the posterior spinal cord and are more infiltrative than ependymomas and therefore difficult to resect completely. Tumoral cysts are often eccentrically located within the spinal cord and are small and irregular. The benign cysts or syrinxes are either rostral or caudal to the tumor and have smooth walls.
Imaging Features
Magnetic resonance imaging of astrocytomas may be radiographically indistinguishable from ependymomas. Full diameter cord involvement and homogenous high T2 signal intensity favor the diagnosis of astrocytoma. Most astrocytomas present as ill-defined diffuse fusiform enlargement of the cord at the time of diagnosis. They are isointense to slightly hypointense on T1WIs and hyperintense on T2WIs (Fig. 4A, B ). Although low grade, nearly all astrocytomas enhance after contrast administration with a uniform or heterogeneous enhancement pattern. Contrast enhancement helps to delineate the tumor from edema, cysts, and syrinxes. The actual tumor margins may extend beyond the enhancing margins. Tumoral cysts enhance, whereas the lining of the syrinx does not enhancement. Syringomyelia is more common in the pilocytic type.
FIGURE 4: Astrocytoma. Astrocytomas are more infiltrative than ependymomas with extensive edema, and the "cap sign" is absent, as hemorrhage is uncommon. A, Sagittal fast spin echo image demonstrates an ill-defined, heterogenous high T2 signal intensity lesion. B, Postcontrast sagittal T1WI demonstrates heterogenous enhancement with cystic components.
Treatment
Lesions arising in the cervical cord may present with neck weakness or, left untreated, may cause quadriplegia, dependent on the level of impingement. Thoracic involvement requires a sensory, rather than motor examination to clinically localize the tumor. Both sensory and motor impairment are seen with lumbar ependymomas.
Astrocytomas are more infiltrative than ependymomas and therefore are difficult to completely resect with higher rates of reoccurrence. Prognosis is predicted by the histological grade and is usually worse than ependymomas. Survival for astrocytoma is lower than ependymomas.21 22
Radiation therapy is generally not indicated for low-grade astrocytomas of the spine but has a role in higher-grade astrocytomas and lower-grade tumors where en bloc resection was limited.23
The most important predictor of postoperative outcome is preoperative neurological status.24-26
Ganglioglioma
Gangliogliomas, a rare subtype of spinal cord astrocytomas are composed of a mixture of neoplastic mature neuronal elements (ganglion cells) and neoplastic glial elements, primarily astrocytic. They are relatively benign tumors with slow growth and late clinical presentation. The course is typically more indolent in children than in adults. There is a tendency for local reoccurrence and metastasis.27,28
Imaging Features
Scoliosis and bony remodeling (erosion/scalloping) are more common than with astrocytomas or ependymomas. Other differentiating features include holocord and long-cord segment involvement, mixed signal on T1WI, prominent tumoral cyst, and patchy enhancement extending to the cord surface, lack of edema, and absence of hemosiderin.29
Treatment
Treatment options generally follow that of spinal astrocytomas.
Hemangioblastoma
Spinal hemangioblastomas are uncommon and account for approximately 1% to 5% of spinal cord tumors. As with their intracranial counterpart, one third of the cases have an association with Von Hippel-Lindau syndrome. Up to 20% may be multiple.20
These tumors are usually discrete small and are very vascular and usually associated with enlarged feeding arteries and draining veins.
Imaging Features
Lesions are located mainly on the dorsal surface of the cord. The typical MR appearance is that of a large intramedullary cyst with a mural nodule. The spinal cord is often diffusely enlarged, out of proportion to the solid component of the tumor nidus. The edema may extend far beyond the solid tumor and may in part be due to venous congestion or anterio-venous shunting. These cord changes should resolve after tumor resection.
Hemangioblastomas have the largest syrinx formation compared with the other intramedullary tumors. Symptomatic small hemangioblastomas have relatively large associated syrinxes, whereas asymptomatic lesions often do not.30
The signal intensity of hemangioblastomas is variable on T1WIs and hyperintense on T2WIs (Fig. 5A-C ). Associated cysts may have signal intensity similar to CSF or higher signal intensity on T1WIs because of high protein content. The tumor nodule enhances intensely after contrast administration (Fig. 5D ). Serpentine flow voids corresponding to large feeding or draining vessels can be seen on both T1WI and T2WI along the dorsal aspect of the cord and can simulate a vascular malformation.
FIGURE 5: Hemangioblastoma. A-B, Sagittal fast spin echo T2WIs show a relatively large associated syrinx within the cervical and thoracic cord. C, Sagittal T1WI demonstrates variable signal intensity of associated cysts. Slightly higher T1 signal intensity is noted in the more inferiorly located cyst due to higher protein content. D, Postcontrast T1WI demonstrates intense enhancement of the solid portion of the tumor with tumor vascularity dorsally that can mimic an anterio-venous malformation.
Newer techniques including fast 3-dimensional contrast-enhanced MRA have been successful in demonstrating the vascular supply of these tumors, reducing the need for conventional angiography.
Treatment
Angiography is indicated for large neoplasms when the diagnosis is indeterminate on MRI and preoperative embolization may be useful in select cases to limit intraoperative blood loss.31,32 33
The differential diagnosis includes other vascular tumors such as paragangliomas and metastatic renal cell carcinomas in patients with Von Hippel-Lindau syndrome.34
Lymphoma
Lymphoma is not limited to a single spinal compartment. Spinal cord involvement is usually metastatic; primary non-Hodgkin lymphoma of the central nervous system (CNS) is infrequent in the spinal cord.20
Imaging features
Lymphoma demonstrates solid enhancement with adjacent high T2 signal intensity consistent with edema. Cord enlargement is not as severe as with other intramedullary neoplasms.
Treatment
Treatment for spinal lymphoma parallels that of intracranial lymphoma: chemotherapy, steroids, and radiotherapy. Serial MRIs may be used to categorize response into 4 groups: complete response (resolution of all contrast-enhancing tumor), partial response (50% decrease in the measurement of contrast-enhancing tumor), stable disease (<50% decrease or <25% increase), and progressive disease (>25% enlargement).35
Metastasis
Intramedullary metastases are rare. Less than 2% of cancer patients at autopsy had intramedullary involvement of their primary neoplasms.36
Imaging Features
Magnetic resonance has greatly facilitated the diagnosis of intramedullary metastases. On T1WIs, metastatic lesions are isointense to spinal cord and hyperintense on T2WIs and enhance after contrast administration (Fig. 6A-D ). Metastases are usually smaller than primary cord tumors and the cord may be of normal size. Cysts are rarely noted. The surrounding edema is out of proportion to the size of the tumor. Melanoma metastases may be high on T1WIs as a result of melanin or hemorrhage.
FIGURE 6: Intramedullary metastases. A, Axial T1WI of the brain demonstrates a metastatic lesion from primary testicular cancer. B, Sagittal T2WI shows extensive nodular intraspinal masses and thickened nerve roots of the cauda equina. C, Sagittal T1WI demonstrates a grossly widened thecal sac and poor definition of normal CSF density. D, Postcontrast sagittal MR image shows extensive leptomeningeal tumor spread.
Treatment
Treatment depends on the primary neoplasm, as this dictates chemotherapy regimen and possible radiation. Palliative or debulking surgery may be performed as well as spinal stabilization surgery as necessitated.
Rare Tumors
Primitive neuroectedermal tumors in the intramedullary compartment usually are caused by subarachnoid seeding/leptomeningeal deposit, secondary to their propensity for extensive spread through the central nervous system. When an intracranial PNET is diagnosed, screening of the spine with MR is standard to evaluate for extent. These tumors are more common in adults.37
Treatment
Surgery, radiation therapy, and chemotherapy are the standard of care, yet prognosis remains extremely poor.38,39
Intradural/Extramedullary Tumors
Magnetic resonance imaging is excellent for evaluating and delineating intradural tumors, both intramedullary and extramedullary. The range of tumors found in the intradural/extramedullary space is few in comparison with bony or central cord tumors. Most of these masses originate from a systemic/congenital disorder such as the phakomatoses or are metastasis such as drop metastasis from the brain.
Nerve Sheath Tumors
Nerve sheath tumors comprise schwannomas and neurofibromas and represent 30% intradural/extramedullary tumors. The peak incidence is in the fourth and fifth decade. Symptoms may be present for more than 2 years before diagnosis as there is usually little functional impairment. There is no sex predilection, unlike meningiomas, which occur more frequently in women.40,41
Schwannomas and neurofibromas are histologically distinct tumors but indistinguishable by imaging standards. Both are composed of Schwann cells. Schwannomas almost always arise form the dorsal sensory roots and form well-encapsulated firm masses that compress adjacent tissue without invading the involved nerve. Neurofibromas are more complex and are composed of Schwann cells mixed with fibroblasts and the parent nerve. They are unencapsulated, often fusiform and enlarge within the nerve itself.
In the spine, schwannomas are more common than neurofibromas and are typically solitary. Nerve sheath tumors that are multiple in the spine frequently are associated with neurofibromatosis, both types 1 and 2 (Fig. 7A-D ); 70% are intradural/extramedullary; 15% are extradural or both intradural extramedullary in a dumbbell configuration, whereas less than 1% are intramedullary.20
FIGURE 7: Multiple nerve sheath tumors in a patient with NF-2. A, Axial fast spin echo T2 in a patient with NF-2 demonstrating a paraclinoid calcified meningioma and cerebellopontine angle tumor. B-C, Axial and coronal T1-weighted MR images demonstrate bilateral vestibular schwannomas. These patients are also prone to develop peripheral and spinal schwannomas. D, Postcontrast T1WI demonstrates multiple enhancing intradural/extramedullary and extradural foraminal tumors.
Nerve sheath tumors are most frequent in the thoracic spine (40%) with an equal incidence in the cervical and lumbar spine (30%).40,41
The lesions are usually benign and although the mass may expand the spinal neuroforamen or erode the vertebral bodies, surgery is not necessary unless the patient has symptoms such as nerve root impingement/radiculopathy. Surgery typically results in good outcomes.42
Malignant nerve sheath tumors represent approximately 10% of all nerve sheath tumors and require excision regardless of symptoms (Fig. 8A, B ). These tumors may present malignant degeneration after radiation therapy or as sequelae of NF-1.43
FIGURE 8: Neurofibrosarcoma in a patient with NF-1 is heralded by a rapid increase in pain and size of the lesion. In NF-1, nerve sheath tumors are always neurofibromas. A, Axial gradient echo image shows the dumbbell-shaped intraspinal and foraminal nerve sheath tumors with malignant degeneration of the largest posterior paraspinal tumor. B, Postcontrast coronal T1WI demonstrates enhancing lesions which extend through the intervertebral foramina at almost every level in addition to the large soft tissue mass lesion. Larger lesions are prone to malignant degeneration.
Imaging features
Plain films and CT may demonstrate foraminal enlargement, pedicular erosion, posterior vertebral scalloping, thinned lamina, or a paravertebral soft tissue mass (Fig. 9A ). "Twisted ribbon" ribs and kyphoscoliosis are associated with NF-1. The nerve sheath tumors appear cystic and may mimic the density of CSF and are indistinguishable from lateral thoracic meningoceles or nerve root sleeves on CT.
FIGURE 9: Solitary schwannoma. A, Axial CT shows a large soft tissue mass extending into the spinal canal, with associated bony scalloping and widened neural foramen, typical of a nerve sheath tumor. B-C, Sagittal T1WI and T2WI show an expansile lesion of heterogenous signal intensity scalloping the vertebral body with foraminal extension. D, Postcontrast axial T1WI demonstrates intense enhancement of the lesion with a few nonenhancing cystic components.
Neurofibromas and schwannomas have similar T1 and T2 signal characteristics as well as enhancement patterns and cannot be reliably distinguished from each other by MRI. On T1WIs, these tumors are isointense to slightly hypointense to spinal cord (Fig. 9B ). On T2WIs, they are heterogeneously hyperintense without a dural tail (Fig. 9C ). Cystic areas may appear more hyperintense. A "target pattern" with peripheral high T2 signal intensity and a central low T2 component may be seen. The low T2 signal intensity is due to hemorrhage, collagen, and densely packed Schwann cells. Heterogeneous enhancement is noted on postcontrast images (Fig. 9D ).
Differential diagnosis includes metastases, meningiomas, chordomas, and hemangiomas.
Treatment
Schwannomatosis is a rare tumor syndrome characterized by the presence of multiple schwannomas without the stigmata of NF-1 or NF-2.44
Meningiomas
Meningiomas comprise approximately 25% of primary intraspinal tumors and are second only to nerve sheath tumors in frequency. There is a female predominance of 4 to 10:1. They usually present after the fourth decade. Spinal cord meningiomas are believed to originate from meningothelial cells near the dorsal root ganglia. Most (90%) of the meningiomas are intradural extramedullary, whereas only 5% are extradural.20
The most common location is the thoracic region (80%), 15% in the cervical, and 5% in the lumbar spine. In men, the distribution in the thoracic and cervical spine is about equal. Approximately two thirds of thoracic meningiomas occur in the dorsal spinal canal, whereas in the cervical spine, 85% occur ventrally.
Spinal meningiomas are slow-growing tumors that produce signs and symptoms by progressive compression of the spinal cord and adjacent nerve roots.
The histological classification of spinal meningiomas is similar to their intracranial counterpart. Majority are meningothelial or psammomatous in type.45
A recent study showed that less than 2% of meningiomas are malignant.46 47
Imaging features
Unlike intracranial meningiomas, spinal meningiomas may not be associated with secondary osseous changes. Foraminal widening and pedicular erosion may occasionally be present. The tumor may be calcified, and heavy calcification may be seen (Fig. 10A ).
FIGURE 10: Intraspinal meningiomas. A, Axial CT demonstrates dense tumoral calcification which is associated with a poor postoperative course, due to greater difficulty in complete excision. B, Coronal T2-weighted MR shows low T2-signal intensity of the calcified component. C-D, Postcontrast coronal and axial T1WIs demonstrate avid enhancement of the noncalcified intradural portion and only mild enhancement on the calcified component of the tumor with associated cord compression.
Meningiomas are usually discrete lesions, with a broad dural based and typically isointense to spinal cord on T1WIs and hypointense on T2WIs. Calcification results in low T1 and low T2 signal intensity (Fig. 10B, C ). These tumors are usually solitary and enhance avidly and homogenously (Fig. 10D ). A dural tail may be seen. Neurofibromatosis type 2 is associated with multiple meningiomas.
The differentiation may be determined by evaluating for neurofibromas that are heterogeneous on T2WIs and enhance more intensely than meningiomas.48
Treatment
Incidental, asymptomatic meningiomas, particularly in patients older than 65 years, may be observed for a year to verify stability. Surgery is not necessarily required. Resection is indicated if the mass becomes symptomatic or demonstrates growth. Radiotherapy plays a role in limiting recurrence.
Paragangliomas
Spinal paragangliomas are slow-growing, well-encapsulated, intradural/extramedullary tumors and are usually found in the conus medullaris, cauda equina, and filum terminale.
Imaging features
On MRI, they are isointense to spinal cord on T1WIs and hyperintense on T2WIs. Hemorrhage, prominent serpiginous vascular flow voids and a salt-and-pepper appearance and intense enhancement are characteristic findings.
Developmental Lesions (Dermoid and Epidermoid Cysts, Teratomas and Lipomas)
Dermoids and epidermoids are inclusion tumors and constitute 1% to 2% of intraspinal tumors. These tumors are more frequently encountered in children (10%-17%).49
Epidermoids occur more commonly in the cranium, unlike dermoids which occur more frequently in the spine. Most spinal epidermoids (approximately 60%) occur in the lower thoracic and lumbar spine and dermoids occur most frequently in the lumbosacral region (60%). Intramedullary teratomas, tumors of multipotential cells producing tissues that represent a mixture of 2 or more germinal layers, are very rare in adults. Teratomas are classified as mature, immature, or malignant based on the degree of differentiation. Diagnosis is made on histopathologic basis. Differential diagnosis includes other cystic lesions such as dermoids and epidermoids.
Surgery is the primary treatment modality. Radical resection is not recommended because of the usually benign nature of tumor and low recurrence rates even in subtotal resections. Adjuvant therapy is only indicated if histopathology reveals malignant components.
Most spinal lipomas (60%) are intradural in a subpial location with secondary intramedullary extension. The incidence of intraspinal lipomas not associated with spina bifida is approximately 1%.50,51 52
Imaging Features
Epidermoids have signal intensity similar to CSF on both T1WI and T2WI. Rarely, they may be heterogenous and demonstrate high T1 signal intensity as well as peripheral rim enhancement. Dermoids have more heterogenous signal characteristics with areas of high T1- and corresponding low T2 signal intensity secondary to secretions from sebaceous glands, liquid lipid metabolites, and cholesterol (Fig. 11 ).
FIGURE 11: Benign teratoma of the conus medullaris. A, Sagittal T1WI demonstrates a complex intradural mass at the conus medullaris consisting of isointense and hyperintense components in a young patient. No dorsal dermal tract was present. B, Sagittal fast spin echo T2WI shows low T2 signal intensity corresponding to the high T1 component. C, Postcontrast T1WI with fat-saturation technique demonstrates mild enhancement.
Lipomas are hyperintense on T1WIs and relatively low on T2WIs and suppress on fat suppressed images (Fig. 12A-C ).
FIGURE 12: Subpial lipoma. A-C, Axial T1, sagittal T2WI and STIR image demonstrate a subpial lipoma located on the right lateral aspect of the conus.
Treatment
Resection is indicated in tethered cord or when neurological symptoms dictate, particularly in the pediatric population to prevent neurological deterioration. Lipomas are often adherent to the spinal cord, extending superficially into the substance of the cord making them surgically unresectable.
Metastases
Intradural/extramedullary leptomeningeal carcinomatosis is rare. The CNS drop metastases are more common in children than adults. PNETs are the most common primary CNS malignancy; systemic cancers that produce leptomeningeal metastases are breast (36%), lymphoma (28%), lung (16%), and melanoma (10%).49,53
The lumbar spine is the most frequent location of leptomeningeal metastases which is attributable to gravitational effects. Three serial CSF samples may be required to obtain a positive CSF cytology for malignant cells.
Patients may be asymptomatic or present with nonspecific neurological symptoms including back pain, extremity weakness, radiculopathy, sensory dysfunction, and bowel and bladder incontinence. Leptomeningeal metastases are the first presentation of systemic malignancy in approximately 9% of cases and correlates with poor prognosis.
Imaging Features
Contrast-enhanced MRI is excellent for evaluation of leptomeningeal carcinomatosis and has largely replaced CT myelography.54
T1-weighted images demonstrate heterogenous CSF signal intensity and nerve root enlargement. Tumor nodules are isointense to spinal cord on T1WIs and are barely visible on the T2WIs. On postcontrast T1WIs, enhancement of the meninges, nerve roots, and surface of the cord can be seen (Fig. 13A-C ). The nerve root enhancement may be thick and linear or nodular.
FIGURE 13: Intradural extramedullary and intramedullary metastases from primary testicular malignancy. A, B, Sagittal T1WI and T2WI demonstrate heterogenous intramedullary and intradural masses, cord expansion, and cord edema. C, Postcontrast T1WIs show multiple enhancing intrapsinal masses.
Differential diagnosis of leptomeningeal enhancement includes inflammatory conditions such as sarcoidosis, meningitis, and arachnoiditis. Nerve root enlargement may also be due to edema secondary to compression, Guillain-Barre syndrome, or primary hypertrophic radiculopathies such as Charcot-Marie-Tooth.
Extradural Tumors
Extradural tumors are the most frequent of the spinal tumors. They primarily comprise osseous vertebral lesions and may be primary or metastatic. The overwhelming number of extradural tumors are metastatic lesions; primary bone tumors account for less than 5%.55
Primary benign extradural tumors
Hemangioma
Hemangioma is by far the most common benign tumor of the axial skeleton, occurring in 11% of spines at autopsy.56
Imaging features.
Computed tomography will detect the honeycomb or polka-dot pattern of thickened trabeculae (Fig. 14A ).
FIGURE 14: Vertebral body hemangioma. A, Axial CT showing thickened trabeculae giving rise to a polka-dot or honeycomb pattern, a characteristic feature of hemangiomas. B-C, Sagittal T1WI and sagittal T2WI show hyperintense signal intensity in the vertebral body and posterior elements with bony expansion. D, Sagittal T1WI after contrast and with fat-saturation technique demonstrates minimal enhancement of the lesion, indicating presence of a predominantly fatty component.
Atypical hemangiomas are rare, less than 1% of vertebral hemangiomas, but can cause collapse of vertebral collapse with extension into the epidural space resulting in pain and radiculomyelopathy. Although CT is technically excellent for bony changes, MR is indicated for evaluation of possible nerve root or cord involvement. If T1 signal is high, the lesion is considered benign (Fig. 14B-D ). If the lesion is shown to have low T1 and T2 signal, this may represent degenerative change/involution of the lesion, and observation is usually sufficient. If low T1 and high T2 signal is evident, this may represent an atypical hemangioma, necessitating further imaging (Fig. 15A-D ).
FIGURE 15: Aggressive hemangioma. A-B, Sagittal T1WI and T2WI demonstrate predominantly low T1 and high T2 signal intensity within the vertebral body and posterior elements with a dorsal epidural soft tissue component producing cord compression and cord edema. C, Postcontrast T1WI demonstrates enhancement of the vertebral body and also delineates the entire extent of the posterior epidural soft tissue component. D, Axial CT confirms coarsening of the bony trabecular pattern and lack of frank of cortical destruction. This excludes malignancy.
A negative bone scan would exclude malignant degeneration of an atypical hemangioma; a positive bone scan is concerning for malignancy, and histopathologic correlation should be performed along with metastatic workup.
Treatment.
As most hemangiomas are benign and found incidentally that no intervention is usually required. If surgery is indicated, angiography is occasionally needed to demonstrate tumor vascularity before embolization, as these tumors are highly vascular.
Osteoid Osteoma/Osteoblastoma
Osteoid osteomas account for about 6% of benign spinal tumors. A total of 10% arise from the vertebral column, of which 75% involve the posterior elements. The lumbar spine is most commonly affected, followed by the cervical spine. The classic symptom is pain accentuated at night, relieved by anti-inflammatory agents. Painful scoliosis in a child should alert the diagnosis of osteoid osteoma.
Osteoblastomas are related to osteoid osteomas and by definition are larger than 1.5 cm in diameter. Osteoblastomas are relatively rare and represent only 1% of primary bone tumors but represent 10% of spinal osseous tumors. The pain is often duller than that associated with osteoid osteomas. A much rarer malignant form of osteoblastoma exists and is histologically determined.
Imaging features.
The radiolucent vascular nidus (with central calcification) surrounded by bony sclerosis on plain film radiography and CT is diagnostic of osteoid osteoma (Fig. 16A ); MR findings are nonspecific. The intense enhancement of the nidus and enhancing reactive soft tissue mass may mimic a spinal Brodie abscess or malignancy (Fig. 16B, C ). Bone scintigraphy is highly sensitive for osteoid osteoma and reveals intense nidal uptake, sometimes with a rim of lesser uptake corresponding to the surrounding bony sclerosis.
FIGURE 16: Osteoid osteoma. A, Axial CT shows the calcified nidus adjacent to the lateral mass and subtle reactive sclerosis of the adjacent vertebral body. B, Axial fast spin echo T2WI demonstrates high T2 signal intensity in the vertebral body. C, Postcontrast axial T1WI shows enhancement of the vertebral body with extension of the inflammatory process into the neural foramina. This can mimic a spinal Brodie abscess.
On MRI, osteoblastomas are more variable in signal than osteoid osteomas. They are expansile osteolytic lesions and may have an epidural component (Fig. 17A, B ). The tumor is usually low to intermediate on T1WIs and mixed to high signal intensity on T2WIs. They may show enhancement after gadolinium administration (Fig. 17C-E ).
FIGURE 17: Osteoblastoma. A-B, Axial CT and postcontrast axial T1WIs demonstrate an expansile destructive lesion involving the C2 vertebra and the posterior elements with an epidural component. C, Sagittal T1WI demonstrates the expansile destructive lesion involving C2 and the posterior elements. D, Sagittal fast spin echo T2WIs lack fluid-fluid levels that are typically seen in aneurysmal bone cysts. E, Postcontrast T1WI demonstrates intense enhancement of the lesion and delineates the posterior epidural and smaller prevertebral soft tissue component.
Treatment.
Treatment for osteoid osteoma and osteoblastoma is excision which provides pain relief as well as improvement or even resolution of spinal deformity.57 58 59 60,61
Aneursymal Bone Cyst
Aneurysmal bone cysts (ABCs) are nonneoplastic processes characterized by an expansile and aggressive bone lesion with multiloculated blood spaces. They may arise at a site of prior spinal trauma or may be induced by anomalous vascular process.62
Frequently (up to 32%), they may arise within a preexisting lesion particularly a GCT but also osteosarcoma, osteoblastoma, and chondroblastomas or fibrous dysplasia.
Imaging.
Plain films demonstrate bony expansion and remodeling with a thin bony rim and internal septations. Computed tomography and magnetization transfer show the characteristic multilocular, cystic expansile mass with fluid-fluid levels. High T1 signal may reflect the hemorrhagic component.
The differential diagnosis of fluid-fluid levels in the presence of a solid component includes GCTs, osteoblastomas, osteosarcomas, and chondroblastomas.
Treatment.
Angiography may be useful preoperatively or as a primary treatment modality, ie, embolization.63 64 65
Giant Cell tumor
Giant cell tumors account for 5% to 10% primary bone tumors, 7% of which may be spinal in location. Most spinal GCTs arise from the sacrum. Vertebral body lesions may extend to the posterior elements and can be locally aggressive and extend into disk space and adjacent vertebral bodies.
Imaging Features.
The radiographic hallmark is an expansile lytic lesion without a marked sclerotic border. Both solid and cystic components may be present in addition to areas of hemorrhage. Solid lesions are intermediate signal intensity on T1WIs and are often hypointense on T2WIs due to high collagen content. The low T2 signal intensity is helpful to differentiate it from other common sacral lesions such as chordomas, metastases, and plasmacytomas which are hyperintense on T2WIs. Secondary aneurysm bone cysts may form due to hemorrhage and may be evident on CT and MR as fluid-fluid levels.
Treatment.
Complete surgical resection remains the treatment of choice, but local recurrence is commonly attributed to limited resection secondary to its invasive tendencies. Lesions that cannot be entirely excised are treated with a combination of surgical curettage and radiation therapy. Radiation therapy may decrease both spread and reoccurrence.66
Incomplete resection of a vertebral body GCT may result in malignant transformation. Malignant conversion typically occurs after radiation of benign lesions and is seen in about 10% of cases.
Osteochondroma
Osteochondroma is overall the most common benign osseous tumor but is relatively rare in the spine. Half of all spinal ostechondromas are identified in the cervical spine with C2 being the most commonly affected.67
Imaging Features.
The radiological and pathological hallmark of osteochondroma is continuity of the lesion with the marrow and cortex of the underlying bone. In the spine, they are usually sessile but may be pedunculated arising from a broad base from the posterior elements. The advantage of MR lies in its capability of visualizing the cartilaginous cap overlying the apex of the bony excrescence. A cap thickness of greater than 2 cm is worrisome for malignant transformation. Indications for surgical intervention include development of pain due to persistent growth after skeletal maturity and increasing cartilage cap size to greater than 2 cm. The MR appearance of the cartilage portion is increased signal on T2WIs; the calcified portion is low signal on both T1WI and T2WI.
Treatment.
Surgical excision of osteochondroma is usually curative.
Primary Malignant Extradural Tumors
Chordoma
Chordomas account for 2% to 4% primary bone tumors and arise from notochordal remnant tissue. The most common location is the sacrococcygeal region where 50% of spinal chordomas are located, followed by the sphenooccipital region (25%-40%) and remaining spine (15%). Vertebral body lesions are more likely to metastasize than sacral or skull base lesions.
These tumors lesions arising from the vertebral bodies can extend across the adjacent disc space and the sacroiliac joint mimicking infection.
Imaging Features.
Radiographically, chordomas are midline, destructive lesions. Both plain film and CT reveal a destructive, lytic (or mixed lytic/sclerotic) lesion of the sacrum with an associated presacral or retrosacral mass. Amorphous calcification may be seen in 50% to 70% of cases.
On MR, most chordomas are isointense or low signal intensity compared with muscle on T1WIs and hyperintense on T2WIs. A dumbbell or mushroom configuration of the tumor can be seen in cervical lesions mimicking a nerve sheath tumor. The internal fibrous septa that divide the gelatinous components of the tumor are depicted as low signal intensity on T2WIs and are a characteristic feature. Chordomas usually enhance to a moderate degree.
Magnetic resonance is useful to demonstrate the soft tissue component and osseous involvement, epidural extent of disease, and relationship to vascular structures especially in the cervical spine.
Treatment.
Surgical resection is the mainstay of treatment followed by radiation therapy. These lesions are not considered amenable to chemotherapy.68,69 70,71
Chondrosarcomas
Chondrosarcomas are the second most common nonlymphoproliferative primary spine tumor in adults. A total of 5% to 10% are found in the spine, mostly in the thoracic spine. Lesions may be exophytic especially if they arise from osteochondromas. Clinical and biological behavior and imaging features depend on histological grade.
Imaging Features.
Radiographically, bone destruction is noted with a chondroid matrix with an associated soft tissue mass, the latter usually with advanced disease. If no soft tissue component is present, the vertebral body lesion may be primarily lytic with sclerotic margins. Lesions may cross the disc space to involve an adjacent vertebral body.
The MRI reveals osseous and soft tissue involvement as low to intermediate signal on T1WIs and hyperintensity on T2WIs. Areas of mineralization remain low signal on all pulse sequences. After gadolinium administration, enhancement is usually avid in a ring and arc-like septal pattern.
Treatment.
These tumors are slow growing and relatively resistant to radiation and chemotherapy, and because of their tendency to recur locally, lesions of the vertebral column have a relatively poor prognosis.72
Osteosarcoma
Osteosarcoma is the third most common primary spinal bone tumor.73 20
Imaging Features.
Radiographically, osteosarcomas tend to be osteoblastic giving rise to an "ivory vertebra." On MR, the signal intensity is usually low on both T1WI and T2WI.
Treatment.
Spinal osteosarcomas tend to be more refractory to treatment than those arising in the limb.74 68 75
Ewing sarcoma and PNET
These tumors are the most common nonlymphoproliferative bone tumors in children. Overall, these tumors are more prevalent in the adult population.37
Imaging Features.
Imaging features of Ewing Sarcoma and PNETs on MR are nonspecific. Vertebral lesions can mimic other tumors such as eosinophilic granuloma, aggressive hemangiomas, lymphomas, metastases, ABCs, and GCTs. Paraspinal soft tissue involvement is typical.
Treatment.
As with most extradural neoplasms, en bloc surgical resection is standard. These tumors respond well to radiotherapy and chemotherapy for additional benefit. There is also a role for the use of neoadjuvant chemotherapy.76
Metastases
Neoplasms that frequently metastasis to the osseous spine include myeloma, breast, lung, prostate, and lymphoma/leukemia. Lung cancer is the most frequent neoplasm to metastasis to the spine followed by breast cancer.36 77
Neuroblastoma is the most common to tumor to metastasize to the spine in the pediatric population. These tumors may insinuate themselves into the bony spine by direct extension from the retroperitoneum or may metastasis hematogenously (Fig. 18A, B ).
FIGURE 18: Metastatic neuroblastoma. A-B, Postcontrast coronal T1WI demonstrates bilateral neuroblastomas arising from the adrenal glands in addition to an enhancing left paraspinal mass with neuroforaminal extension.
Myeloma takes many forms in the spine including plasmacytoma; multiple myeloma is by far the most common form and represents almost half of all spinal tumors (Fig. 19A-C ).
FIGURE 19: Diffuse multiple myeloma. The normal marrow process is completely replaced by the infiltrative process. A-B, Sagittal STIR image and T1WI show diffuse marrow inhomogeneity throughout the thoracic spine. C, Postcontrast sagittal T1WI with fat saturation demonstrates patchy enhancement.
Magnetic resonance is the best imaging modality for detecting and characterizing metastatic disease, but bone scintigraphy is more useful in detecting multiple lesions and distant metastases. The MR is useful for diagnosis, staging , evaluating complications, and treatment planning.
Imaging Features.
Typically, single or multiple discrete lesions of variable size are identified as low signal intensity on T1WIs and are hyperintense on T2WIs (Fig. 20A, B ). Sclerotic metastases may be low on T2WIs. Noncontrast T1WIs and STIR are the most useful sequences. The "hyperintense disc sign" on T1WIs is a reliable indicator of marrow replacement.78 Fig. 20C ). For further verification, fat-saturated images with contrast can be performed.
FIGURE 20: Diffuse metastatic disease. A, Sagittal T1WI demonstrates patchy low T1 signal intensity, the multiple vertebral bodies and the isodense epidural soft tissue component. B, Sagittal STIR demonstrates high T2 signal intensity of the involved vertebral bodies with better delineation of the circumferential epidural soft tissue mass and associated cord compression. C, Postcontrast sagittal T1WI is particularly useful for delineating the extent of epidural disease.
Lesions demonstrating bright signal intensity on precontrast T1WIs are almost always benign and may be due to normal marrow conversion, hemangioma, or sequelae of radiation or chemotherapy, myelofibrosis, or degenerative changes in older patients. Normal marrow should not enhance after contrast administration.
Low T1 signal and normal marrow on T2WI and STIR image may simply be a reflection of conversion to red marrow and can be seen in anemia, renal disease or chronic obstructive pulmonary disease, high altitude, smokers, or obesity.
Treatment.
Considered incurable, significant palliation may be achieved using a tailored approach that may include radiation therapy, radiopharmaceuticals,79 80 81 82
Neuroblastoma metastasis may compress the cord requiring immediate radiation for palliation.83 84 85
Therapy for multiple myeloma targets treating the myelodysplastic disorder and preventing bone loss with the use of bisphosphonates.86 87,88 89,90
FUTURE APPLICATIONS
Surveillance of bone tumors is dependent on age of the patient, type of tumor, initial stage at diagnosis, and institutional preference. Many papers have described oncological staging of spinal tumors, which is dependent on clinical, imaging, and histopathologic features. Extensive discussion in the literature on treatment of these tumors may be found. Outcomes of spinal cord tumors are most dependent on survival statistics and preoperative neurological status. There are very few papers discussing standards for surveillance, particularly using MR for follow-up evaluation of spinal tumors.
For metastatic medulloblastoma in children, a recent study showed that absence of reoccurrence in the central nervous system obviated surveillance of the spine using MR, as the risk was virtually excluded.91 92
Evidenced-based protocols using MR for surveillance of treated spinal cord tumors is an interesting and necessary area of future research.
CONCLUSION
The MRI is the preoperative modality of choice in the evaluation of tumors of the spinal cord and spinal column. Magnetic resonance can narrow the differential diagnosis and guide surgical resection. Familiarity with "pseudotumors" or benign conditions mimicking a tumor of the spinal axis is important to avoid unnecessary biopsy. Radiological assistance is playing a bigger intraoperative role with the advances of intraoperative imaging including ultrasound and MR. Surgical resection, in conjunction with chemotherapy and radiation therapy is still the mainstay for treatment of spinal tumors. Presurgical treatment may incorporate chemoembolization in the future as well as more individually targeted chemotherapies and immunotherapies (such as vaccine Oncophage in the case of multiple myeloma metastases). Additional research is needed in standardizing imaging protocols for surveillance of spinal tumors.
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